Key players in the cash for honours inquiry

Once Scotland Yard decided to investigate whether Labour had sold honours in return for the cash to fund its 2005 election campaign, it was inevitable that Lord Levy would be at the centre of police attention.

The former music mogul remains Labour's chief fundraiser and is regularly in No 10 as well as being the PM's personal envoy to the Middle East.

In July 2006 Lord Levy turned up by appointment at Colindale police station in north London, and was arrested under two anti-corruption laws. The first was the Honours (Prevention of Abuses) Act 1925 and the second the Political Parties, Elections and Referendums Act 2000.

The 1925 law was passed after the scandal surrounding Lloyd George selling titles for Liberal party funds. The 2000 act demands that parties must disclose donations. Before the last election Labour raised £14m in loans in an arrangement that the party treasurer, Jack Dromey, did not know about.

Lord Levy's first arrest led to police seizing documents and computer files from his business address, including documents, letters and emails relating to Labour lenders. He was again questioned in September for more than 90 minutes.

In the early stage of the investigation one area of interest for police was the four businessmen who had lent Labour money and subsequently been recommended by Tony Blair for peerages in 2005. The honours were blocked by the Lords Appointments Commission.

Four of the nominees - Barry Townsley, Chai Patel, Sir David Garrard and Sir Gulam Noon - lent Labour a total of £4.25m before the 2005 election.

The Guardian has previously reported how police have been studying an email from Mr Blair's chief of staff, Jonathan Powell, discussing honours, in which he suggests: "ML will not be happy about this." The implication is that Lord Levy was regarded as having a voice in giving honours.

In January 2007 Lord Levy was arrested for a second time, but on this occasion he was detained on suspicion of conspiracy to pervert the course of justice.

Lord Levy is represented by the tough defence solicitor Neil O'May, from the human rights law firm Bindman's. After the first arrest, which Mr O'May said was unnecessary because his client had been fully cooperating, the solicitor was steadfast about Lord Levy's innocence: "He has not been charged and does not expect to be once this inquiry is complete, as he has committed no offence. He denies any wrongdoing or any involvement in wrongdoing with others."

The investigation continues to dog him, however. Just a week ago there was a potentially unfortunate coincidence at a Jewish community event, a group for which Lord Levy has raised generous sums of money. At the community security trust dinner, he was sitting at the top table. Also there was the commissioner of the force pursuing him, Sir Ian Blair.

Ruth Turner: Downing Street's director of external relations

Downing Street's director of external relations was arrested at dawn on January 19 on suspicion of perverting the course of justice, thrusting the shy aide to the prime minister into the centre of a maelstrom.

A month and a day after that arrest, Ms Turner answered police bail. Detectives had more questions for her and she was again released on bail, pending further inquiries.

Though one of the youngest members of the Downing Street staff, she has a responsible position: she is one of the gatekeepers to No 10 and a link to the Labour party and outside world.

Her arrest was one of the surprise turns in the inquiry, and led to claims, categorically denied by Downing Street, that it was maintaining a second, secret, email system not disclosed to the police.

Instead, the focus on Ms Turner appears to be because of a document written by her for her lawyers. This was passed to detectives and is a central part of Scotland Yard's inquiry. It is said to refer to a meeting she had with Lord Levy last summer.

Police are investigating whether Lord Levy was asking Ms Turner to shape her evidence for the police. Lord Levy denies the claims. Ms Turner has always denied any wrongdoing and Downing Street has expressed its support for her.

Jonathan Powell: PM's chief of staff

Tony Blair's chief of staff has been interviewed at least once under criminal caution, meaning that he is a potential suspect. It is expected he may be interviewed for a second time by detectives examining how honours were awarded.

One document in particular makes Mr Powell of interest to Scotland Yard. An email from him about honours says: "[Michael Levy] will not be happy about this," possibly meaning that Labour's chief fundraiser was involved in decisions about honours.

As chief of staff, Mr Powell is of interest to both parts of the investigation. He would have knowledge of how decisions were taken on the awarding of honours, while also possessing knowledge useful to the second part of Scotland Yard's investigation into an alleged cover-up.